1. Field of the Invention
The present invention relates to a control device and a control method that are applied to an internal combustion engine in which a fuel cutoff operation is performed to cut off fuel supply to a combustion chamber.
2. Description of Related Art
Conventionally, an internal combustion engine is provided in which a fuel cutoff operation is performed while a specific condition is fulfilled (while the accelerator pedal operation amount for the internal combustion engine is zero, for example) in order, for example, to improve the fuel efficiency of the internal combustion engine. In this kind of an internal combustion engine, the amount of fuel may be adjusted to accomplish various purposes when a fuel cutoff operation is terminated to restart the supply of fuel to the combustion chambers.
For example, one of related art control devices for internal combustion engines (which may also be hereinafter referred to as “related art device”) is applied to an internal combustion engine that is provided with a catalyst which cleans the gas (exhaust gas) from the combustion chambers, and controls the amount of fuel so that the air-fuel ratio of the air-fuel mixture that is burned in the combustion chambers becomes richer than the stoichiometric air-fuel ratio when a fuel cutoff operation is terminated to restart the supply of fuel to the combustion chamber. The related art device can thereby adjust the amount of oxygen that is stored in the catalyst (oxygen storage amount) and maintain a state in which the catalyst can clean the exhaust gas with high efficiency (refer to Japanese Patent Application Publication No. 2007-255355 (JP 2007-255355 A), for example).
As described above, the related art device controls the amount of fuel (in other words, the air-fuel ratio of the air-fuel mixture) after the termination of the fuel cutoff operation in view of the exhaust gas cleaning efficiency of the catalyst. More specifically, the air-fuel ratio of the air-fuel mixture has an influence on the amount of oxygen that is contained in the exhaust gas that is generated when the air-fuel mixture is burned. Thus, the oxygen storage amount of the catalyst can be adjusted by controlling the air-fuel ratio of the air-fuel mixture (by adjusting the air-fuel ratio to be richer than the stoichiometric air-fuel ratio as described above, for example) in view of the amount of oxygen that is contained in the exhaust gas that is introduced into the catalyst.
On the other hand, the air-fuel ratio of the air-fuel mixture, in general, also has an influence on the torque that is output from the internal combustion engine (which may also be hereinafter referred to as “output torque”). Thus, when the air-fuel ratio of the air-fuel mixture is adjusted to be richer than the stoichiometric air-fuel ratio after the termination of the fuel cutoff operation, the output torque after the fuel cutoff operation becomes higher than the output torque before the fuel cutoff operation. In other words, the output torque increases after the fuel cutoff operation is terminated.
The degree of change in output torque as described above (which may also be hereinafter referred to as “torque variation”) is considered to depend on various parameters (for example, the air-fuel ratio after the fuel cutoff operation is terminated, and features of the internal combustion engine such as engine displacement, cylinder arrangement and firing order). Therefore, it may be considered that depending on the parameters, the magnitude of torque variation does not necessarily become so large as to substantially affect the operation of the internal combustion engine. However, it is desirable to reduce the magnitude of torque variation as much as possible.